Impervious cover increases the quantity of runoff by keeping stormwater from soaking into the ground naturally. Increased volumes and velocities of runoff then erode stream channels and reduce the health of existing streams. Water runs more rapidly off of an impervious area causing flooding to become both more common and more intense downstream. Meanwhile, with less water soaking into the ground, water tables can drop and streams and wells fed by groundwater can begin to dry up.

The Virginia Department of Environmental Quality is requiring every jurisdiction in the state to update existing stormwater development criteria with new, tougher development standards by April 1, 2014, with a go live date of July 1, 2014. As a result of the modifications to existing code being mandatory, the City is also taking this opportunity to streamline all stormwater regulations by placing them under a single section of City Code, Chapter 35, Stormwater.

The tougher standards outlined herein include the state’s minimum requirements and those proposed by the City of Falls Church. The criteria are being implemented as part of the state-wide effort to restore water quality to the Chesapeake Bay. These values stem from scientific research on stormwater runoff and the pollution it generates in the form of phosphorus.

Impervious cover increases the quantity of runoff by keeping stormwater from soaking into the ground naturally. Increased volumes and velocities of runoff then erode stream channels and reduce the health of existing streams. Water runs more rapidly off of an impervious area causing flooding to become both more common and more intense downstream. Meanwhile, with less water soaking into the ground, water tables can drop and streams and wells fed by groundwater can begin to dry up.

The 35% cap on impervious coverage was a surrogate for water quality controls on phosphorus. The proposed 0.41 standard has an equivalency of 14-16% impervious coverage. This means development exceeding the 0.41 pounds of phosphorus-per-acre-per-year standard must treat stormwater using Best Management Practices (e.g. rain gardens, cisterns, infiltration trenches) before it leaves the site. The 35% cap is no longer needed as a water quality performance standard. However, the city plans to add lot coverage limits in Chapter 48, Zoning under an amendment to the proposed ordinance.

In the same manner as the existing ordinance, the new stormwater performance criterion only applies to properties that disturb 2,500 square feet of land. The difference between the two is that the proposed ordinance substantially increases the level of pollutant reduction required. The most common examples of site work that triggers this regulation are large additions to homes and infill development. When the land disturbance threshold of 2,500 square feet is exceeded developers must prepare an engineered plan, which includes stormwater management calculations demonstrating compliance with the regulations.

In April 2013 City Council approved the Stormwater Utility Fund, which is an enterprise fund with a dedicated revenue source that can only be used for stormwater expenditures. A fee will be assessed to each property within the city based on units of 200 square feet of impervious cover (e.g. roof, driveway, walkway, and patio).

The effect of the new ordinance will be an increase in the number of Best Management Practices installed in the city and subsequently a reduction of pollutants entering the city’s stormwater conveyance system. The reductions in pollutants count toward the city’s obligations for cleaning up the Chesapeake Bay. The modest reductions from development will help the city by having to spend less capital funds treating stormwater runoff.

The stormwater ordinance only regulates projects under construction. Private development is not required to solve existing drainage problems; however they must demonstrate problems will not being exacerbated. The ordinance does provide additional tools for the city engineer to regulate sheet flow on developments – an area the current ordinance is silent on. Only concentrated flow is currently regulated for potential erosion and flooding.

The proposed ordinance grandfathers projects submitted to the city prior to July 1, 2014. This date is preliminary since the ordinance has not been passed. It is possible City Council will adopt an earlier date.

Visit the City of Falls Church stormwater section to learn more about stormwater runoff, how it impacts water quality in the Chesapeake Bay and water quantity (flooding) in Falls Church, and how to mitigate stormwater runoff on your site and get credit toward the stormwater utility fee.